Evaluation of evaporation from Lake Ontario during IFYGL by a modified mass transfer equation

An improved bulk transfer technique was developed for large‐lake evaporation based upon recent boundary layer research near the air‐water interface. A variable bulk transfer coefficient, dependent upon atmospheric stability, is given as a function of the nondimensional wind speed gradient, the potential temperature gradient, and the Monin‐Obukhov length. The technique, which requires the same data as the simplified mass transfer equation, can be readily applied to large lakes throughout the world. This technique has been applied to the Lake Ontario data set collected during the International Field Year for the Great Lakes. The inclusion of stability increases calculated evaporation during the unstable high‐evaporation months and decreases calculated condensation during the stable late spring months to more realistic levels. Comparisons between the Lake Hefner mass transfer equation and the technique recommended here indicate that the mass transfer equation may overestimate Lake Ontario evaporation by approximately 20%.

Section: Wind Speed and Stability Analysissupporting

confidence: 78%

An improved aerodynamic evaporation technique for large lakes with application to the International Field Year for the Great Lakes

Quinn¹

1979

“…include atmospheric stability efl•cts and applied to Lake Ontario [Phillips, 1978;Quinn, 1979] and Lake Superior [Derecki, 1981]. Although based on diffusion theory, the major limit to this method is that its results depend upon the mass transfer coefficient, an empirical parameter that has to be calibrated to independent local data sets of evaporation rates.…”

Section: Different Methods Of Estimating Evaporation Rates Have Been mentioning

confidence: 99%

“…Evaporation is also a cooling process which involves transfer of both mass and heat across the air-water interface. It can therefore be evaluated either from a related mass transfer equation or by means of an energy balance equation.include atmospheric stability efl•cts and applied to Lake Ontario [Phillips, 1978;Quinn, 1979] and Lake Superior [Derecki, 1981]. Although based on diffusion theory, the major limit to this method is that its results depend upon the mass transfer coefficient, an empirical parameter that has to be calibrated to independent local data sets of evaporation rates.…”

mentioning

confidence: 99%

Evaporation from Lake Kinneret: 1. Eddy correlation system measurements and energy budget estimates

Assouline¹,

Mahrer²

1993

Evaporation rates over Lake Kinneret were directly and continuously measured by means of the eddy correlation system (ECS) for the relatively long periods of 20 and 44 days at the beginning and end of the summer (first and second periods), respectively. Results clearly show that wind speed and stability of thermal stratification over the water surface strongly affect evaporation from the lake. Consequently, large differences in measured daily evaporation rates were apparent during both periods. Evaporation rates, estimated by the energy budget method (EBM) were compared with the corresponding values measured directly by the ECS. Large differences were found between the estimated hourly evaporation rates and the measured ones, in both the values and the timing of maximal rates. In addition, the EBM calculated negative nocturnal evaporation rates, while the ECS measured positive values. Differences between estimated and measured evaporation rates monitored on a daily basis were also noted. The differences were larger for the first period, characterized by sharav events denoting climatic instability. High evaporation rates resulting from strong winds were not depicted by EBM estimates. The distributions of hourly evaporation rates over a 24 hour period or of the daily rates over an entire period as estimated by the EBM were very similar to those of net radiation, while corresponding distributions resulting from ECS measurements were very similar to those of wind speed. The daily average evaporation rate for the first period, calculated by the EBM, was smaller than the corresponding value resulting from ECS measurements. When applied on a hourly basis, the EBM gave a much more similar estimate. For the second period, there were no significant differences between the daily average based on the computed values (for both daily and hourly intervals) and the corresponding average based on the measured ones. INTRODUCTIONGreat effort has been invested in developing tools to measure, model and simulate the evaporation process over free water surfaces. One of the main goals of this intensive research is to accurately evaluate water loss from lakes due to evaporation. When evaporation is of the same magnitude as precipitation and runoff, it becomes a significant component of the lake's hydrologic cycle. Its determination is crucial to lake level forecasts, and essential to its regulation and to the definition of optimal management policies conceming lake water resources. Different methods of estimating evaporation rates have been applied to lakes. Since evaporation is in fact a loss of water, it can be evaluated via the lake's water budget. However, such a method is only reliable in caseswhere all the components in the water balance equation are available, and of the same order of magnitude and accuracy, thereby eliminating the possibility of large residual errors in the computed evaporation. Evaporation is also a cooling process which involves transfer of both mass and heat across the air-water interface. It can therefore be ...

“…Great Lakes evaporation studies typically used mass transfer formulations from the classic Lake Hefner study [U.S. Geological Survey, 1954, 1958 [see Richards and Irbe, 1969]. More recently, Phillips [1978] and Quinn [1979] included atmospheric stability effects on Great Lakes evaporation bulk transfer coefficients; the latter approach is used presently by both Canadian and U.S. agencies applied to monthly data for surface temperatures, wind speed, humidity, and air temperatures [Derecki, 1981;Quinn and Kelley, 1983…”

Section: Great Lakes Evaporation Modelmentioning

confidence: 99%

Verifiable evaporation modeling on the Laurentian Great Lakes

Croley¹

1989

Water or energy balance estimates of Great Lakes evaporation require storage change data, not available in simulations or forecasts, and errors in the components of the balances are summed in the residual, giving large estimation errors. Neither these balance estimates nor evaporation models, which use the aerodynamic equation with mass transfer coefficients developed originally in the Lake Hefner studies, can be verified, since independent estimates of evaporation are not available with sufficient accuracy. However, water surface temperatures can be used to verify energy budgets. The mass transfer coefficient research is combined here with lumped concepts of classical energy conservation and a new superposition heat storage model to provide continuous simulation capability of both water surface temperatures and lake evaporation for use in outlooks and forecasts of lake levels. Calibration matches remotely sensed water surface temperatures for those Great Lakes with observations over the past 20 years. Model sensitivities are analyzed and heat and water budgets are compared. _ ß Mollurod • J F M AM J J A $ O N D